Implementation of the ManagedRuntime interface that searches
through a set of known JNDI locations and method invocations to locate the
appropriate mechanism for obtaining a TransactionManager.
Built in support is provided for the following Application Servers:

AutomaticManagedRuntime

getTransactionManager

Return the TransactionManager for the managed runtime. This
manager is used to register synchronization listeners, to
map transactional PersistenceManagers to the current transaction,
and possibly to enlist XA resources.